1. Field of the Invention
This invention relates to sprung arch roofs or crowns of continuous glass melting furnaces, and more particularly to the problems resulting from the non-uniform temperatures encountered during heat-up of the furnace which cause portions of the overall structure, as well as the individual bricks employed in constructing the arched refractory roofs, to expand at different times.
2. Description of the Prior Art
Conventionally, sprung arch roofs as employed in continuous glass melting furnaces spring from skews running the entire length of the furnace; the skews being set on heel plates firmly attached to the buckstays forming part of the furnace superstructure. Conventionally, the roof is built up of individual, tapered, like-sized refractory bricks which may be set in an overlapping pattern like the checker pattern of a conventional brick wall. An example of such a roof is shown in U.S. Pat. No. 2,236,920 issued on Apr. 1, 1941. The construction of such roof may be accomplished by simply dipping the individual bricks in a siliceous mortar and setting them in place on a form supported by scaffolding. When the form on which the roof has been laid during construction is removed, the slight elastic yielding of the buckstays and tie rods, together with the bedding-in of the contacting surfaces of adjacent bricks against each other, allows the crown of the roof to drop slightly and small gaps to open between the lower ends of the bricks. Thereafter, when the furnace is heated up, the bricks expand and raise the crown to its original position.
Newly constructed roofs as above-described are often very damp, and they are slowly dried out over a period of time (10 to 12 days), by temporary burners such as salamanders placed at convenient locations about the furnace. During this time, the temperature throughout the furnace and the roof will not be uniform. It is the usual practice in glass melting furnaces to construct the arches of silica bricks, which exhibit their maximum thermal expansion at low temperatures such as those encountered during the drying-out period. Accordingly, it may be found that the bricks expand at different times or the crown may warp during the drying-out period by rising unequally in one part or another with respect to the plane or symmetry of the tank. Consequently, as heating occurs and the bricks dry out, some may become sufficiently loose to drop from the roof arches into the interior of the furnace.
In the past, bricks dropping out of the roof have been replaced by driving larger, wedge-shaped bricks into the openings after the original bricks have fallen, with the new bricks being initially held in place due to their larger size, and then by their expansion as heat-up continues. This procedure is not entirely satisfactory in that it requires the insertion of a cold, larger size brick into an arch of the heated bricks, causing the pressure on the bricks to be increased as the heat-up continues since the ends of the arches are held in a fixed position by the skrew backs. As a result, the bricks may spall or be crushed and a section of the roof may fall. Another disadvantage is that it is necessary to retrieve the fallen bricks from the tank so that they will not contaminate the glass to be produced therein.